Hydrophilic polar analytes are notoriously difficult to extract and preconcentrate from aqueous matrices. Sample preconcentration is of utmost importance in the trace analysis of these recalcitrant analytes. A variety of extraction-based preconcentration techniques have been utilized for this purpose (Fontanals, R. M. Marce, F. Borrull, J. Chromatogr. A 1152 (2007) 14). With the current trend of miniaturization in analytical instrumentation, microextraction techniques are gaining popularity. Microextraction techniques include solid phase microextraction (SPME) (Pawliszyn, S. Liu, Anal. Chem. 59 (1987) 1475; Belardi, J. Pawliszyn, Water Pollut. Res. J. Can. 24 (1989) 179), hollow fiber microextraction (Zhang, J. Poerschmann, J. Pawliszyn, Anal. Commun. 33 (1996) 219), single-drop microextraction (Jeannot, F. F. Cantwell, Anal. Chem. 69 (1997) 235), liquid phase microextraction (He, H. K. Lee, Anal. Chem. 69 (1997) 4634), extraction techniques based on suspended particles, membranes/disks, coated vessel walls, etc. (Lord, J. Pawliszyn, J. Chromatogr. A 885 (2000) 153), and stir bar sorptive extraction (SBSE) (Baltussen, P. Sandra, F. David, C. Cramers, J. Microcolumn Sep. 11 (1999) 737). SPME techniques include traditional fiber SPME (Pawliszyn & Liu, Anal. Chem. 59 (1987) 1475; Belardi & Pawliszyn, Water Pollut. Res. J. Can. 24 (1989) 179; Arthur & Pawliszyn, Anal. Chem. 62 (1990) 2145) and in-tube SPME (Eisert & Pawliszyn, Anal. Chem. 69 (1997) 3140; McComb, et al., Talanta 44 (1997) 2137; Hartmann, et al., Bull. 7 (1998) 96; Kataoka &Pawliszyn, Chromatographia 50 (1999) 532).
In particular, fiber SPME and in-tube SPME (Eisert, J. Pawliszyn, Anal. Chem. 69 (1997) 3140; McComb, R. D. Oleschuk, E. Giller, H. D. Gesser, Talanta 44 (1997) 2137; Hartmann, J. Burhenne, M. Spiteller, Fresenius Environ. Bull. 7 (1998) 96) capillary microextraction (CME) (S. Bigham, J. Medlar, A. Kabir, C. Shende, A. Alli, A. Malik, Anal. Chem. 74 (2002) 752) have experienced an explosive growth over the past two decades, due in part to research by Pawliszyn and co-workers (Pawliszyn & Liu, Anal. Chem. 59 (1987) 1475) which provided a significant step toward automation of sample preparation in chemical analysis. Another significant reason behind such growth lies in the fact that these techniques pose little risk to human health and the environment by completely eliminating the use of organic solvents in the extraction process. Moreover, CME uses a sorbent coating located inside a small diameter tubing either in the form of a surface coating or a packed/monolithic sorbent bed. Thus, analytes are directly extracted onto the sorbent coating/bed from a sample as they pass through the tubing (Eisert, J. Pawliszyn, Anal. Chem. 69 (1997) 3140).
In addition to its use in GC, (Arthur, et al., Anal. Chem. 64 (1992) 1960), high-performance liquid chromatography (HPLC) (Eisert & Pawliszyn, Anal. Chem. 69 (1997) 3140; Chen & Pawliszyn, Anal. Chem. 67 (1995) 2530) SPME is also suitable for other hyphenation, such as supercritical fluid chromatography (Hirata & Pawliszyn, J. Microcol. Sep. 6 (1994) 443), capillary electrophoresis (CE) (Figeys, et al., Nat. Biotechnol. 14 (1996) 1579; Whang, & Pawliszyn, Anal. Commun. 35 (1998) 353), mass spectrometry (MS) (Zhang, & Pawliszyn, Anal. Chem. 65 (1993) 1843), and inductively coupled plasma mass spectrometry (ICP-MS) (Moens, et al., Anal. Chem. 69 (1997) 1604). It is portable and is especially suited for field analysis (Pawliszyn, Sampling and Sample Preparation for Field and Laboratory. Elsevier: New York; (2002)).
However, fiber SPME suffers from unresolved problems, which include fiber breakage, mechanical damage of the coating during operation and handling of the SPME device, and limited sample capacity. These issues led to the development of in-tube SPME (Eisert & Pawliszyn, Anal. Chem. 69 (1997) 3140) also called capillary microextraction (Bigham, et al., Anal. Chem. 74 (2002) 752). In this new format, the sorbent coating is placed on the capillary inner wall. Analytes are extracted by passing the sample through the coated capillary (Lord & Pawliszyn, J. Chromatogr. A 885 (2000) 153). In-tube SPME has a significant advantage over traditional fiber SPME in that the sorbent coating is protected against mechanical damage during operation since it is secured on the inner wall of a capillary. Short segments of GC columns have been used to perform extraction by in-tube SPME (Kataoka &. Pawliszyn, Chromatographia 50 (1999) 532).
Additionally, CME easily couples with HPLC, allowing easier analysis of weakly volatile or thermally labile analytes (Mullett, J. Pawliszyn, J. Sep. Sci. 26 (2003) 251). CME also offers some other advantages over fiber SPME. SPME fibers often have limited sample capacities. Higher sample capacities can be obtained with CME because the sorbent coating/bed is contained within a longer segment of the tube providing higher sorbent loading. Fiber SPME devices also have issues with mechanical stability—the fiber can break, the coating can be scratched, and the needle can bend (Djozan, Y. Assadi, S. Haddadi, Anal. Chem. 73 (2001) 4054). CME devices allow for superior mechanical stability because flexible capillaries with outer protective coatings are utilized, providing safeguard against mechanical damage to the sorbent or the tubing.
Conventionally coated GC capillaries for in-tube SPME still limit sample capacity due to diminutive, sub-micrometer thickness of GC coatings, as well as reduced thermal and solvent stability due to a lack of chemical bonds between the coatings and the capillary wall. To address these issues, Malik and co-workers introduced sol-gel capillary microextraction (CME) (Bigham, et al., Anal. Chem. 74 (2002) 752) representing in-tube SPME on fused silica capillaries with surface-bonded sol-gel hybrid organic-inorganic coatings. The use of the capillary format and the covalently bonded sol-gel coating helped overcome the format-related shortcomings of conventional fiber SPME as well as the thermal and solvent stability issues of traditional sorbent coatings.
Ionic liquid (IL)-mediated sol-gel hybrid organic-inorganic materials present enormous potential for effective use in chemical analysis. This opportunity, however, has not yet been explored. One obstacle to materializing this possibility arises from the high viscosity of ILs significantly slowing down sol-gel reactions. This work overcame this hurdle and successfully prepared IL-mediated advanced sol-gel materials for capillary microextraction (CME). In IL-mediated sol-gel processes, ILs are responsible for porous morphology of the created sol-gel materials. However, IL-generated porous morphology alone is not enough to provide effective extraction media; chemical characteristics of both the organic polymer and the precursor play important roles. The present invention teaches how to make proper choices for these ingredients to ensure highly efficient IL-mediated organic-inorganic hybrid extraction media with desired sorbent characteristics.
In recent years, ionic liquids (ILs) (organic salts that melt at or below 100° C.) have gained popularity in a number of fields due to their perceived advantages over traditional solvents. They are considered “green” solvents because they are remarkably less hazardous than their conventional counterparts thanks to negligible vapor pressures, low flammability, good thermal stability, “tunable viscosities,” low corrosion tendencies, and varying degrees of solubility with water and organic solvents (S. A. Forsyth, J. M. Pringle, D. R. MacFarlane, Aust. J. Chem. 57 (2004) 113). These properties have led to the use of ILs in a variety of areas including green chemistry (N. V. Plechkova, K. R. Seddon, In Methods and Reagents for Green Chemistry; P. Tundo, A. Perosa, F. Zecchini, Eds.; Wiley: Hoboken, N.J., (2007) 105-130), organic synthesis and catalysis (T. Welton, Chem. Rev. 99 (1999) 2071; R. Sheldon, Chem. Comm. 23 (2001) 2399; C. M. Gordon, Appl. Catal. A 222 (2001) 101; J. Dupont, R. F. de Souza, P. A. Z. Suarez, Chem. Rev. 102 (2002) 3667; D. B. Zhao, M. Wu, Y. Kou, E. Min, Catal. Today 74 (2002) 157), chemical industry (N. V. Plechkova, K. R. Seddon, Chem. Soc. Rev. 37 (2008) 123), electrochemistry (D. R. Macfarlane, M. Forsyth, P. C. Howlett, J. M. Pringle, J. Sun, G. Annat, W. Neil, E. I. Izgorodina, Acc. Chem. Res. 40 (2007) 1165; R. Hagiwara, J. S. Lee, Electrochemistry 75 (2007) 23; D. Wei, A. Ivaska, Anal. Chim. Acta 607 (2008) 126; P. Hapiot, C. Lagrost, Chem. Rev. 108 (2008) 2238), amino acid and peptide chemistry (J. C. Plaquevent, J. Levillain, F. Guillen, C. Malhaic, A. C. Gaumont, Chem. Rev. 18 (2008) 5035), carbohydrate chemistry (0. A. El Seoud, A. Koschella, L. C. Fidale, S. Dorn, T. Heinze, Biomacromolecules 8 (2007) 2629), and in the preparation of microemulsions (Z. M. Qiu, J. Texter, Curr. Opin. Colloid Interface Sci. 13 (2008) 252). Several books and extensive reviews have been also published on ionic liquids and their applications (S. Chowdhury, R. S. Mohan, J. L. Scott, Tetrahedron 63 (2007) 2363; P. Wasserscheid, T. Welton, Ionic Liquids in Synthesis, 2nd ed.; Wiley-VCH: Weinheim, Germany (2008); H. Weingartner, Angew. Chem. Int. Ed. 47 (2008) 654).
ILs have also found applications in a number of areas in analytical chemistry, including GC (D. W. Armstrong, L. F. He, Y. S. Liu, Anal. Chem. 71 (1999) 3873; J. L. Anderson, In Ionic Liquids in Chemical Analysis; M. Koel, Ed.; CRC Press: Boca Raton, Fla. (2009) 139-165), LC (L. J. He, W. Z. Zhang, L. Zhao, X. Liu, S. X. Jiang, J. Chromatogr. A 1007 (2003) 39; R. Kaliszan, M. P. Marszall, M. J. Markuszewski, T. Baczek, J. Pernak, J. Chromatogr. A 1030 (2004) 263; M. P. Marszall, R. Kaliszan, Crit. Rev. Anal. Chem. 37 (2007) 127; A. M. Stalcup, In Ionic Liquids in Chemical Analysis; M. Koel, M. Ed.; CRC Press: Boca Raton, Fla. (2009) 168-183), countercurrent chromatography (A. Berthod, S. Carda-Broch, Anal. Bioanal. Chem. 380 (2004) 168), CE (E. G. Yanes, S. R. Gratz, M. J. Baldwin, S. E. Robinson, A. M. Stalcup, Anal. Chem. 73 (2001) 3838; M. Vaher, M. Koel, M. Kaljurand, Electrophoresis 23 (2002) 426; W. D. Qin, S. F. Y. Li, Analyst 128 (2003) 37; M. Lopez-Pastor, B. M. Simonet, B. Lendl, M. Valcarcel, Electrophoresis 29 (2008) 94), analytical spectroscopy (C. D. Tran, Anal. Lett. 40 (2007) 2447), liquid-liquid extractions (J. G. Huddleston, H. D. Willauer, R. P. Swatloski, A. E. Visser, R. D. Rogers, Chem. Comm. 16 (1998) 1765; M. Gharehbaghi, F. Shemirani, M. Baghdadi, Int. J. Environ. Anal. Chem. 89 (2009) 21), solid-phase extraction (G. V. Myasoedova, N. P. Molochnikova, O. B. Mokhodoeva, B. F. Myasoedov, Anal. Sci. 24 (2008) 1351), micro-solvent cluster extraction (T. Charoenraks, M. Tabata, K. Fuji, Anal. Sci. (2008) 1239), SPME (J. F. Liu, N. Li, G. B. Jiang, J. M. Li, J. A. Jonsson, M. J. Wen, J. Chromatogr. A 1066 (2005) 27; Y. N. Hsieh, P. C. Huang, I. W. Sun, T. J. Whang, C. Y. Hsu, H. H. Huang, C. H. Kuei, Anal. Chim. Acta 557 (2006) 321; F. Zhao, Y. Meng, J. L. Anderson, J. Chromatogr. A 1208 (2008) 1), single-drop microextraction (L. Vidal, A. Chisvert, A. Canals, A. Salvador, J. Chromatogr. A 1174 (2007) 95), and supercritical fluid extraction (S. Keskin, D. Kayrak-Talay, U. Akman, O. Hortacsu, J. Supercrit. Fluids 43 (2007) 150). Extensive reviews have been published in on IL applications in the areas of analytical chemistry (S. Pandey, Anal. Chim. Acta 556 (2006) 38; X. Han, D. W. Armstrong, Acc. Chem. Res. 40 (2007) 1079; M. Koel, Ionic Liquids in Chemical Analysis; CRC Press: Boca Raton, Fla.; (2009)).
Recently, ILs have been used in the preparation of sol-gel materials (S. Dai, Y. H. Ju, H. J. Gao, J. S. Lin, S. J. Pennycook, C. E. Barnes, Chem. Commun. 3 (2000) 243; Y. Zhou, J. H. Schattka, M. Antonietti, Nano Lett. 4 (2004) 477; Y. Liu, M. J. Wang, Z. Y. Li, H. T. Liu, P. He, J. H. Li, Langmuir 21 (2005) 1618; Y. Liu, M. J. Wang, J. Li, Z. Y. Li, P. He, H. T. Liu, J. H. Li, Chem. Commun. 13 (2005) 1778; M. A. Klingshirn, S. K. Spear, J. D. Holbrey, R. D. Rogers, J. Mater. Chem. 15 (2005) 5174; H. F. Wang, Y. Z. Zhu, X. P. Yan, R. Y. Gao, J. Y. Zheng, Adv. Mater. 18 (2006) 3266; A. Karout, A. C. Pierre, J. Non-Cryst. Solids 353 (2007) 2900; H. F. Wang, Y. Z. Zhu, J. P. Lin, X. P. Yan, Electrophoresis 29 (2008) 952). In sol-gel applications, ILs have served as solvents (S. Dai, Y. H. Ju, H. J. Gao, J. S. Lin, S. J. Pennycook, C. E. Barnes, Chem. Commun. 3 (2000) 243; Y. Liu, M. J. Wang, Z. Y. Li, H. T. Liu, P. He, J. H. Li, Langmuir 21 (2005) 1618; A. Karout, A. C. Pierre, J. Non-Cryst. Solids 353 (2007) 2900), pore templates (Y. Zhou, J. H. Schattka, M. Antonietti, Nano Lett. 4 (2004) 477; Y. Liu, M. J. Wang, J. Li, Z. Y. Li, P. He, H. T. Liu, J. H. Li, Chem. Commun. 13 (2005) 1778), drying control chemical additives (M. A. Klingshirn, S. K. Spear, J. D. Holbrey, R. D. Rogers, J. Mater. Chem. 15 (2005) 5174), and possibly as a catalyst (A. Karout, A. C. Pierre, J. Non-Cryst. Solids 353 (2007) 2900). In several cases, ILs had significant effects on the porous structure of sol-gel materials (Y. Zhou, J. H. Schattka, M. Antonietti, Nano Lett. 4 (2004) 477; M. A. Klingshirn, S. K. Spear, J. D. Holbrey, R. D. Rogers, J. Mater. Chem. 15 (2005) 5174; A. Karout, A. C. Pierre, J. Non-Cryst. Solids 353 (2007) 2900), reduction in cracking and shrinking (M. A. Klingshirn, S. K. Spear, J. D. Holbrey, R. D. Rogers, J. Mater. Chem. 15 (2005) 5174; H. F. Wang, Y. Z. Zhu, X. P. Yan, R. Y. Gao, J. Y. Zheng, Adv. Mater. 18 (2006) 3266; A. Safavi, N. Maleki, M. Bagheri, J. Mater. Chem. 17 (2007) 1674) during solvent evaporation from the sol-gel pores, and sol-gel reaction kinetics (M. A. Klingshirn, S. K. Spear, J. D. Holbrey, R. D. Rogers, J. Mater. Chem. 15 (2005) 5174; A. Karout, A. C. Pierre, J. Non-Cryst. Solids 353 (2007) 2900; K. S. Yoo, T. G. Lee, J. Kim, Microp. Mesopr. Mater. 84 (2005) 211; H. Choi, Y. J. Kim, R. S. Varma, D. D. Dionysiou, Chem. Mater. 18 (2006) 5377).
Ionic liquid-mediated sol-gels have only seldom been used in analytical separations. Yan and co-workers utilized IL-mediated sol-gel monoliths in CEC (H. F. Wang, Y. Z. Zhu, X. P. Yan, R. Y. Gao, J. Y. Zheng, Adv. Mater. 18 (2006) 3266; H. F. Wang, Y. Z. Zhu, J. P. Lin, X. P. Yan, Electrophoresis 29 (2008) 952) for the separation of chiral molecules. Racemic mixtures of naproxen (H. F. Wang, Y. Z. Zhu, X. P. Yan, R. Y. Gao, J. Y. Zheng, Adv. Mater. 18 (2006) 3266) and zolmitriptan (H. F. Wang, Y. Z. Zhu, J. P. Lin, X. P. Yan, Electrophoresis 29 (2008) 952) were analyzed using the IL-mediated sol-gel monoliths. In these cases, 1-butyl-3-methylimmidazolium tetrafluoroborate IL was used to assist in a non-hydrolytic sol-gel process to prepare molecularly imprinted silica-based monoliths. The IL might have helped mitigate the sol-gel shrinking problem and acted as a template for pores (H. F. Wang, Y. Z. Zhu, X. P. Yan, R. Y. Gao, J. Y. Zheng, Adv. Mater. 18 (2006) 3266).
Polar sol-gel sorbents have been developed for in-tube SPME including those based on cyano (Kulkarni, et al., J. Chromatogr. A 1124 (2006) 205), crown ether (Zeng, et al., Anal. Chem. 73 (2001) 2429), and poly(ethylene glycol) (Bigham, et al., Anal. Chem. 74 (2002) 75; Wang, et al., J. Chromatogr. A 893 (2000) 157; Silva & Augusto, J. Chromatogr. A 1072 (2005) 7; Bagheri, et al., J. Chromatogr. B 818 (2005) 147; Kulkarni, et al., J. Chromatogr. A 1174 (2007) 50) materials. While these sol-gel coatings have advanced the use of polar organic polymers and achieve higher thermal and solvent stability, these coatings mostly contain long-chain polymers of high molecular weights (Bigham, et al., Anal. Chem. 74 (2002) 75; Wang, et al., J. Chromatogr. A 893 (2000) 157; Silva & Augusto, J. Chromatogr. A 1072 (2005) 7; Bagheri, et al., J. Chromatogr. B 818 (2005) 147) having lower polarity (compared to their short-chain counterparts), and thus, reduced ability to extract highly polar analytes. For such capillaries, sample capacity can still be an issue (Bagheri, et al., J. Chromatogr. B 818 (2005) 147). However, what is needed is a method of developing a matrix having improved analyte absorbance qualities